Method for producing permanently crimped, elastic chemically modified cotton yarns



United States Patent "ice 3,396,530 METHOD FOR PRODUCING PERMANENTLY -CRIMPED, ELASTIC CHEMICALLY MODI- FIED COTTON YARNS Ernst Weiss, Wattwil, Switzerland, assignor to Heberlein Patent Corporation, New York, N.Y., a corporation of New York No Drawing. Filed June 21, 1962, Ser. No. 204,079 Claims priority, application Switzerland, Nov. 13, 1961, 13,129/ 61 8 Claims. (Cl. 57-456) This invention relates to cotton yarns characterized by a permanent crimp and comparatively high elasticity, and also to methods for preparing such yarns.

Permanently crimped, torque or stretch yarns available today comprise continuous filament fully synthetic materials such as the polyamides and the polyesters. These products have achieved commercial significance for use principally in hosiery and the knitting arts and recently as weaving yarns. These stretch yarns are highly practical by reason of the permanent nature of the crimp which can easily be imparted to the fiber material. However, an appreciable number of individuals cannot tolerate direct epidermal contact with fully synthetic fabrics, and ac cordingly blending of the yarn with cotton or regenerated cellulose, which cellulosics are not irritating to the skin, has been necessary in many instances. It will be appreciated that permanently crimped yarns constructed entirely of cellulose or regenerated cellulose would be highly desirable and, by reason of the relatively high cost of polyester and polyamidic fibers, would also be economically very attractive.

Unfortunately, ordinary cotton possesses only very limited thermoplasticity, and accordingly it is impossible to impart any useful crimp to cotton yarns. Techniques for producing permanently crimped or torque stretch nylon yarns, for example, are without effect upon cotton yarn. In fact, the high twisting, heat-setting and subsequent detwisting employed in the production of crimped polyamide yarns produce no useful modification of the physical properties of a cotton yarn simply because cotton has no memory, i.e., is practically not thermoplastic.

Through recent work of Dr. C. H. Fisher at the Southern Regional Research Laboratory of the United States Department of Agriculture chemically modified cotton yarns have been developed which possess appreciable thermoplasticity and which have very favorable textile properties. For a further description of this chemically modified cotton yarn and its method of production reference may be had to Fisher US. patent application Ser. No. 204,299, filed on even date herewith, now abandoned.

It is among the objects of the present invention to produce a novel permanently crimped cotton yarn which has been modified chemically as set forth hereinafter, and to provide methods for permanently crimping such yarns.

The starting yarn in accordance with the present method is a cotton yarn which has been chemically modified. The term chemically modified as employed in the specification and claims of this application shall be understood to mean cotton yarn which has been esterified and/ or etherified to a hereinafter specified minimum extent or degree of substitution. Such preferred chemical modifications include acetylation, cyanoethylation, benzylation and equivalent esterifications and etherifications set forth in the afore-mentioned Fisher application. Quite unexpectedly, slight esterification or etherification greatly increases the thermoplasticity of the fibers of the cotton yarn.

The starting chemically modified yarns herein are preferably acetylated cotton of a degree of substitution of at least about 1.0, cyanoet-hylated cotton of a degree of substitution of at least about 0.4, or benzylated cotton of a Patented Aug. 13, 1968 degree of substitution of at least about 0.2. Degree of substitution refers to the number of OH groups per glucose unit of the cellulose molecule which have been esterified or etherified. The aforementioned minimum degree of substitution is essential in order to impart sufiicient thermoplasticity to the cotton yarn to enable permanent crimping in accordance with the present method and to assure an elasticity in the crimp yarn product equal to at least about 10%, which may be considered to be about a practical minimum in permanently crimped elastic yarns. It is important, of course, that the chemically modified yarn substantially retain its individual fiber structure, and accordingly the extent of the chemical modification must not be such as would appreciably destroy the fiber structure of the formed yarn. It is possible, for example, by the use of low temperature esterification and the exercise of extreme care to acetylate cotton cellulose to a degree of substitution of 3.0 with retention of fibrous character. Such highly substituted yarns are suitable for the purpose of this invention as long as fibrous character of the cellulose is retained after chemical modification.

Typical methods for chemically modifying the cotton yarn, while not forming a part of the present invention, are as follows:

Acetylation A cotton hank roving is wound onto a stainless steel dye tube, pretreated for seventeen hours in a solution containing 99% acetic acid and 1% water. The solution is then drained and the dye tube and cotton roving are imrnersed in a liquid consisting of 54.75% acetic anhydride, 45% isopropyl acetate and 0.25% perchloric acid, where it is allowed to remain for one hour and forty-five minutes at a temperature of 15 C. Following this treatment the acetyl content of the cotton roving is found to be 35.8% by weight, which is equal to a degree of substitution of about 1.5. This is considered a higher acetylated product. A lower acetyl cotton may be prepared by presoaking a cotton yarn for about 2 hours at 60 C. in glacial acetic acid, draining and then reacting for about 1 /2 hours in 25% acetic anhydride, 74.85% acetic acid and 0.15% perchloric acid at about 20 C. The yarn is then drained, washed in tap water and finally at a temperature of about C. The acetyl content of the modified cotton yarn thus produced is between about 23 and 28%.

Benzylation A cotton yarn is wound onto a stainless steel perforated dye tube under very light tension and then saturated with an aqueous caustic soda solution containing 30% NaOH and 1% ethylene glycol by weight. The solution is circulated from the inside to the outside of the package for approximately thirty minutes at about 30 C., then drained off and the package extracted by blowing air through it from the inside out. The benzylation reaction is then carried out by immersing the package in circulating pure benzyl chloride at a temperature of -l00 C. After the desired reaction time the solution is cooled to room temperature, drained and the package is again extracted with air, washed with water at about 60 C. approximately thirty minutes then with a synthetic detergent for approximately thirty minutes and finally again with hot water. The desired degree of substitution is dependent upon the reaction time. The optimum reaction is the point when the flow rate from the inside-out, which will increase steadily to a maximum and then decrease steadily, reaches the same value that was obtained when the reaction was started.

Cyanoethylation Cotton yarn is thoroughly wetted out with a 2% by weight sodium hydroxide solution after which it is centrifuged to approximately 70% wet take-up. The yarn is then reacted in water-saturated acrylonitrile at 65 C. for about thirty to forty-five minutes, whereupon the solution is drained oflf and the yarn carefully washed in an aqueous solution containing 1% phosphoric acid. The yarn is again drained and washed with tap water until all reagents are removed. The nitrogen content of the thus modified cotton yarn is about 45%.

In accordance with the method of the present invention a cotton yarn which has been chemically modified to increase its thermoplasticity is subjected to high twisting and heat fixation or setting in the highly twisted condition during which treatment the filaments of the yarn exhibit a plastic deformation as a result of high twisting. Following high twisting and setting the yarn is untwisted to substantially the same extent that it was initially high twisted; thereby interior torsional tensions are created which are sufficient for the formation of a yarn having a permanent crimp. The treatment thus constitutes a temporary high twisting of the yarn which is preferably accomplished by means of a false twisting device, a variety of which are well known in the art. In such devices the yarn coming from the supply roll passes in succession through a first conveyor, for example a pair of rollers, through a heater or over a heated element, then through the twister of the apparatus, through a second conveyor which again may be a pair of rollers, and finally to a take-up or winding device.

The heating device may comprise a tube through which the yarn passes in axial direction and which is provided with an electrical resistance heating coil. Instead of a tube, a box may be used with several heating coils for simultaneous passage of separate yarns at different points. Also, heat setting of the highly twisted yarn may be accomplished by contact with a heated surface, preferably a metal surface which has been brought to the required temperature electrically.

In accordance with the present invention the temperature employed for heating the yarn depends upon the nature of the cotton fiber material and the thickness of the yarn. Excellent results are obtained with yarns of English numbers to 100 when subjected in highly twisted condition to setting temperatures ranging from about 200 to about 280 C. with the time the yarn is subjected to these elevated temperatures being at least about 0.2 second and preferably between about 0.5 and 5 seconds. It will be appreciated that the coarser the yarn the longer the setting time or the higher the temperature to which the yarn is subjected, with temperature and time being thus inter-related.

Further in accordance with the present invention chemically modified cotton yarns are used which have a low degree of spinning twist corresponding to a twist constant preferably between about 1.5 and 3 and not above a maximum of 4. The twist constant A is calculated in accordance with the formula:

where T is the number of turns per English inch and Ne is the English yarn number.

According to one embodiment of the present method, false twisting and heat setting may be carried out with a single end yarn, in which case the direction of temporary high twisting is the same as the direction of the spinning twist of the yarn so that the staple yarn will not pass through a point of zero twist and thus disintegrate. In this embodiment two single end yarns similarly but separately false twisted and heat-set by high twisting in one direction, for example, may then be doubled and plytwisted in the opposite direction to produce a two-ply crimped yarn. For example two single yarns each with an original spinning twist of 500 turns/meter Z may be separately false twisted in Z-direction and heat-set after which each remains at its original 500 turns/meter Z. These yarns may then be plied in S-direction, for example with about 450 turns/meter S, that is near to the zero point, to produce a two-ply, rather open, voluminous permanently crimpedyarn. Following temporary high twisting and heat-setting the yarns as a rule are given a permanent ply twist in a direction opposite to the direction of its spinning twist. Furthermore it is often of advantage, to simultaneously high twist at least two ends of yarn; the ends of chemically modified cotton yarn will generally be similarly constructed yarns, i.e., of equivalent English yarn numbers and of substantially equivalent twist constants. Thus, for example, two yarns with a spinning twist in Z-direction may be temporarily highly twisted by means of a false twisting device in S-direction past the zero point and thereupon per manently ply-twisted in S-direction. As a result of the simultaneous temporary high twisting of at least two yarns, disintegration and/or undesired loosening of the single ends during passage through the zero point is avoided by wrapping of one ply about the other. The final two-ply crimped yarn thus produced possesses a decreased tendency toward distortion and is a relatively open and voluminous yarn.

In accordance with the present invention the plying twist imparted in the final step of the method may range from about to 500 turns/meter and is as a rule in a direction opposite to the direction of the spinning twist of the starting yarn. The higher the number of ply twist per unit length the closer or tighter will be the filaments of the product. A ply twist up to about 500 turns/meter may be imparted to two or more yarns in cases where a very close, i.e., nonvoluminous, stretch yarn is desired. However, in most instances a voluminous, permanently crimped elastic yarn will be plied to only about 100 to 300 turns/meter.

The crimped yarns of this invention may thus be voluminous or rather close, but in either event they have an attractive and full silkly feel and excellent covering capacity as compared with the uncrimped starting chemically modified yarn or with conventional unmodified cotton yarns. The yarn products hereof further exhibit a relatively great absorptive capacity as compared with fully synthetic yarns of the aforementioned types, which is an important, advantageous physiological property.

The yarn products hereof are also permanently crimped and have an elasticity greater than about 10%, and generally between about 10 and 40%. Elasticity as expressed in percent, often referred to as crimp contraction is determined in accordance with the formula where a is the length of a strand of yarn wetted with water and measured while under a stress of 1.8 g./tex. and b is the length of the same strand after it has been dried in a controlled atmosphere in unstressed condition and then subjected to a stress of 0.018 g./tex. (tex.= grams per 1000 meters).

The best test for determining permanence of the crimp is repeated launderings at elevated temperature to simulate conditions encountered in actual use of fabrics constructed of the yarns of the present invention. These tests are as follows: The crimp may be considered permanent if the crimp contraction is not substantially diminished after a laundering in a solution containing 5 g. of soap per liter at elevated temperature.

The present invention will be further apparent from the following non-limiting examples which illustrate typical methods and products thereof as presently practiced. One of these examples also serves to compare the yarns of the invention with unmodified cotton yarn which has been processed in accordance herewith.

Example 1 Two acetylated cotton yarns with an acetyl content of 36% corresponding to a degree of substitution of 1.5, each of English yarn number 40 and of twist constant equal to 2.5, i.e., a spinning twist of about 600 turns/meter in Z-direction, were temporaritly highly twisted together in a false twisting device to 2100 turns/meter S and heated in the highly twisted condition for a period of 4.1 seconds in a hot air chamber at 240 C. The two yarns were then finally plied and twisted to 240 turns/ meter S. The product was a typically crimped relatively voluminous two-ply yarn having an elasticity or crimp contraction equal to about 21%.

Before crimp contraction is determined, the crimp in the yarn should first be fully developed. Five skeins, each being 8 times the circumference of the reel on which they are wound (preferably 8 meters or yards), should be reeled ofi the cross-wound packages. The tension of the yarn during reeling off should be so controlled that the yarn is straight (approx. 0.9 g./tex.). The skei-ns, irrespective of whether they have been sized or not, should be treated without tension in distilled water at 6070 C. for minutes, hydroextracted with care and dried without tension.

Crimp contraction is determined in the following manner: the skeins on which the crimp has been fully developed are immersed in water at 60 C., containing 2 g./l. of an ordinary wetting agent, for complete wetting out, suspended from a hook, and loaded in a wet condition with 1.8 g./tex. Care should be taken to ensure that skeins are completely smooth when suspended. After the load has been applied for 1 minute, the length of the wet, stretched skeins is measured. The weights are then removed and the skeins are dried at 50-60 C. freely suspended and without any loading. After cooling down for 1 hour in a conditioned room (temperature C., relative humidity 65%), the freely suspended skeins are loaded with 0.018 g./tex. After this load has been applied for 1 minute the length of the skeins is measured. On the basis of these measurements the average crimp contraction was calculated by the aforementioned formula.

A strand of the yarn was subjected to a boiling laundering in a solution containing 5 g. of soap per liter. After this laundering the crimp contraction was not substantially reduced. This shows that the crimp of the yarn is permanent.

Example 2 Three benzylated cotton yarns of a degree of substitution of 0.45 each of English yarn number 60 and a spinning twist in Z-direction equal to a twist constant of 3.9 were led together through a false twisting device, temporarily highly twisted to 2000 turns/ meter S and heated in the highly twisted condition for 4 seconds at 240 C. Following untwisting the three yarns were ply-twisted to 300 tur ns/ meter S. The three-ply yarn thus obtained was found to be substantially more voluminous than a similar three'ply yarn of untreated cotton, and had an elasticity of 10.8%. A strand of the yarn was subjected to a laundering at 60 C. in a solution of 5 g. of soap per liter, whereby the crimp contraction was not substantially reduced. This shows that the crimp of the yarn is permanent.

Example 3 Two 'cyanoethylated cotton yarns containing 3.5% nitrogen, corresponding to a degree of substitution of 0.45, each of English yarn number 10 and a spinning twist in Z-direction equal to a twist constant of 3 were temporarily highly twisted together on a false twisting apparatus to 1100 turns/meter S and exposed in the highly twisted condition for 2 seconds to heated air at 270 C. Subsequently the yarns were ply-twisted to 100 turns/ meter S to produce a two-ply yarn with a full hand. A strand of the yarn was then washed as described in Example 1 whereby the crimp contraction remained practically unchanged.

Example 4 F our acetylated cotton yarns with an acetyl content of about 30-40% each of English yarn number and a spinning twist in Z-direction equal to a twist constant of 3 were temporarily highly twisted together on a false twisting device to 2500 tu-rns/ meter S and while in highly twisted condition passed over a heated metal surface which was maintained at about 250 C. The yarns were in contact with the heated surface for approximately three seconds. Subsequently the four yarns were ply-twisted to 250 turns/meter S. The four-ply yarn thus produced was voluminous, had a full hand, a crimp contraction which is very substantially greater than an analogous four-ply un modified cotton yarn. A strand of the yarn was then washed as described in Example 1, whereby the crimp contraction remained practically unchanged.

Example 5 Two single end yarns of acetylated cotton with an acetyl content of about 3040% each of English yarn number 50 and an original spinning twist of 500 turns/meter Z are separately temporarily highly twisted in a false twisting device to 2000 turns/ meter Z and heated in the highly twisted condition for 2 seconds in a hot air chamber at 270 C. The two yarns are then ply-twisted in S-direction with 300 turns/meter S. The product is a rather open, voluminous permanently crimped two-ply yarn. A strand of the yarn was then washed as described in Example 1 whereby the crimp contraction was not substantially diminished.

Example 6 Two unmodified cotton yarns, each of English yarn number 40, and a twist constant equal to 2.5, spinning twist in Z-direction, were plied and temporarily highly twisted to 2100 turns per meter S, and heated in the highly twisted condition for a period of 4.1 seconds in a hot air chamber at 240 C. Thereafter the two yarns were plytwisted to 240 turns per meter S direction. The product thus obtained was practically not crimped.

As noted hereinabove, chemically modified as employed in the appended claims is intended to mean only cotton yarn which has been either esterified or etherified by acetylation, benzylation or cyanoethylation to a minimum degree of substitution of at least about 1.0, 0.2 and 0.4, respectively, with the degree of substitution in each instance being less than that which would destroy the fibrous character of the cotton.

I claim:

1. A method for producing a permanently crimped chemically modified cotton yarn, which comprises highly twisting a thermoplastic chemically modified cotton yarn, subjecting the yarn in high-twisted condition to temperatures between about 200 and 280 C. for a period sufficient to set the twist therein and subsequently untwisting the so heat-set yarn to substantially the extent of its high twisting, said yarn being esterified or etherified by acetylation, benzylation, or cyanoethylation.

2. A method for producing a permanently crimped chemically modified cotton yarn, which comprises highly twisting in the direction of its spinning twist a thermoplastic chemically modified cotton yarn of English yarn number between about 10 and 100 and having a spinning twist constant of less than about 4, subjecting the yarn in high-twisted condition to temperatures between about 200 and 280 C. for a period suiiicient to set the twist therein and subsequently untwisting the so heat-set yarn to substantially the extent of its high twisting, said yarn being esterified or etherified by acetylation, benzylation, or cyanoethylation.

8. A method as set forth in claim 2- wherein the yarn is a single end, and including the additional step of doubling said twisted, set and untwisted end with another similarly constructed and treated end and ply-twisting said ends in a direction opposed to their spinning twist to about 100 to 500 turns/meter.

4. A method for producing a permanently crimped chemically modified multi-ply cotton yarn, which comprises highly twisting together at least two similarly twisted thermoplastic chemically modified cotton yarns, subjecting the yarns in high-twisted condition to temperatures between about 200 and 280 C. for a period suflicient to set the twist therein, subsequently untwisting the so heatset yarns to substantially the extent of their high twisting and the'n ply-twisting the yarns to about 100 to 500 turns/ meter in a direction opposed to the direction of their spinning twist, said yarns being esterified or ethelified by acetylation, benzylation, or cyanoethylation.

5. A method as set forth in claim 4 wherein the highly twisted yarns are subjected to said elevated temperature for at least about 0.2 second.

6. A method as set forth in claim 4 wherein the direction of high twisting is opposed to the direction of the spinning twist of the yarns.

7. A method for producing a permanently crimped chemically modified cotton yam which comprises temporarily highly twisting a thermoplastic chemically modified cotton yarn by means of a false-twisting device and subjecting the yarn in high-twisted condition to temperatures between about 200 and 280 C. for a period sufficient to set the twist therein, said yarn being esterified or etherified by acetylation, benzylation, or cyancethyl-ation.

8. A method as set forth in claim 4 wherein the hightwisting and untwisting of the yarns is accomplished by means of a false-twisting device.

References Cited UNITED STATES PATENTS 2,980,982 4/1961 Costa et al. 2878 2,999,296 9/1961 Breen et a1 28-78 2,946,181 7/1960 Tissot et a1 57157 3,025,659 3/1962 Stoddard et'al 57156 1,800,944 4/ 1931 Lilienfeld 8-120 2,980,491 4/1961 Segal et a1. 8121 2,993,749 7/1961 Sloan et al. 8121 3,037,902 6/1962 Fahey et al 8121 2,463,618 3/1949 Heberlein et a1. 571;57

FOREIGN PATENTS 665/31 2/ 1931 Australia. 478,259 1/ 1938 Great Britain.

OTHER REFERENCES JOHN PETRAKES, Primary Examiner. 

1. A METHOD FOR PRODUCING A PERMANENTLY CRIMPED CHEMICALLY MODIFIED COTTON YARN, WHICH COMPRISES HIGHLY TWISTING A THERMOPLASTIC CHEMICALLY MODIFIED COTTON YARN, SUBJECTING THE YARN IN HIGH-TWISTED CONDITION TO TEMPERATURES BETWEEN ABOUT 200 AND 280*C. FOR A PERIOD SUFFICIENT TO SET THE TWIST THEREIN AND SUBSEQUENTLY NTWISTING THE SO HEAT-SET YARN TO SUBSTANTIALLY THE EXTENT OF ITS HIGH TWISTING, SAID YARN BEING ESTERIFIED OR ETHERIFIED BY ACETYLATION, BENZYLATION, OR CYANOETHYLATION. 